Engine blow-by test, Blow a bag of blow-by - PeachParts Mercedes-Benz Forum

junqueyardjim · #1 07-09-2007, 01:41 PM

Someone posted yesterday that the best test of engine blowby is with a garbage bag. So I followed another post where the writer was going to test his cars today with a garbage bag. And I wrote that I would do the same. Well I tested mine this morning and now I can't find that thread back and so I decided I would start a new one. Shouldn't mess up some other persons thread with something like this. So the question or project is to measure the amount of time to really fill a 30 gallon garbage bag with blowby. Not a real difficult project for a warm morning. I did it by borrowing a 30 gallon garbage bag from the laundry room. I pulled the hose from the air cleaner grommet, started the car, took the garbage bag in hand and inserted the hose, now above the top of the radiator. It took 2 minutes to get the garbage bag really hard. I held it for a couple more minutes and it didn't seem to get any harder. So, since it didn't stall the engine I presume that the bag developed a leak, though I did not notice a leak. That was on my 85 300D Turbo 617. Then I performed the same test on the 84. A like vehicle, though it is an 84 300D Turbo 617. This is the junkyard car I got from BioPete in Nashville in April. Anyway this car, I ran it for 5 minutes and only had a small blip of air in the bag at that time. I have noticed before that this engine just does not have any blowby. We checked the compression right after we got it started and adjusted the valves. We think it had not been run for 3 or 4 years. Compression was 450 on 3 cylinders, number 2 and 4 were a bit lower, like 375 and 400. Car runs very well, though when starting it cold, even on these summer days, it runs very rough for a couple of seconds after the glow plugs cool off and before piston temperature gets hot. What do you think might be causing that low compression on an engine with no blowby.